Extracts of human lymphocytes analyzed by high-performance liquid chromatography on an anion exchange column showed a major UV-absorbing peak which eluted after the nucleosides and prior to the major nucleotides. This material co-chromatographed with and had the spectral properties of ascorbic acid. Further evidence that the compound was ascorbic acid was obtained with chemical and enzymatic assays. Following its unequivocal identification, we determined the levels of the UV-absorbing compound in chronic lymphocytic leukemia lymphocytes. Normal lymphocytes had 39.6 plus or minus 18.8 nmoles/10 to the 8th power cells (mean plus or minus S.D.). Lymphocytes from patients with chronic lymphocytic leukemia were found to have significantly higher levels (113 plus or minus 52 n moles/10 to the 8th power cells, p less than 0.001.